"What is causing this weekend's winter storm? Let's start from the beginning: Why is so much of the U.S. in for such a powerful winter storm? Essentially, the cause is Arctic air surging southward over the contiguous U.S., just as a low-pressure area is moving eastward, pulling up moisture from the south. When moisture and cold temperatures meet, the result is some combination of snow, sleet and freezing rain."
"A major winter storm is coming together over the U.S., with dozens of states and more than 160 million people likely to be affected by snow, ice and extreme cold from Friday to next Monday. Forecasters so far have some idea of what will happen when the storm arrives: Some areas are in line to see a foot or more of snow, while others will experience freezing rain that will coat everything it touches in a dangerous cloak of solid ice."
A broad surge of Arctic air moving southward is colliding with an eastward-moving low-pressure system that is drawing up moisture from the south. That interaction will produce a mix of snow, sleet and freezing rain across dozens of states, with some locations seeing a foot or more of snow and others coated in dangerous ice. Forecasts for precipitation type and amounts have shifted day to day and hour to hour, reflecting sensitivity to the timing and phasing of cold air and the low. Paying attention to evolving forecasts can improve preparedness.
Read at www.scientificamerican.com
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